Evaluation of the compatibility of building limestones from salt crystallization experiments
Kévin Beck, Muzahim Al-Mukhtar, 2010. "Evaluation of the compatibility of building limestones from salt crystallization experiments", Natural Stone Resources for Historical Monuments, R Přikryl, Á Török
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Salt absorption in porous building stones contributes greatly to the degradation of monuments. Two French porous limestones with similar main characteristics (total porosity, densities and mechanical resistance) were studied: white Tuffeau and Sebastopol stone. Accelerated ageing (weathering) tests were carried out by applying immersion-drying cycles with water containing sodium sulphate or sodium chloride. Samples of the two stones were tested separately and then in sets containing both rock varieties. The results facilitated interpretation of the observed and measured responses of these two limestones to the cycling salt crystallization. The durability of studied stones was evaluated by determining the normalized weight changes during the applied cycles. The Sebastopol stone amplified the amount of salt stored in the Tuffeau with increasing number of cycles performed, inducing its more rapid degradation. Water retention and water transfer in the pore space were found to be two main factors controlling the rate and the type of stone decay due to the salt crystallization.
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Natural stone is considered to be a versatile, durable and aesthetically pleasing building material. From the beginning of civilization, important structures and monuments have been built from, or based on, natural stone. Until the end of the nineteenth century, the use of local stone resources was mostly in balance with the local environment. Strict environmental legislation has resulted in the closing of many long-standing quarries in industrialized countries, which has led to a shortage of traditional stone varieties. This has caused problems for restoration practice. Cheap, imported stone from less industrialized countries has become more widely available in recent years.
Some of the issues related to built stone conservation and restoration covered by this volume are: the establishment of inventories of possible replacement stones; understanding the decay mechanism and use of preventive conservation methods for slowing down decay processes; evaluation of the properties of natural stone; and assessing the risks of using replacement stones of different qualities.